Paper coating composition



Patented Got. 13, 1931 UNITED STATES PATENT OFFICE DONALD B. BRADNER, OF HAMILTON, OHIO, ASSIGNOR TO THE CHAMPION COATED PAPER COMPANY, OF HAMILTON, OHIO, A CORPORATION OF OHIO PAPER COATING COMPOSITION No Drawing.

The present invention relates to the art of coating paper and particularly to an improved paper coating composition. By the term mineral coated paper is meant paper which has been coated with a composition consisting essentially of at least 70% of a mineral pigment, such as clay, satin white, and the like, and not more than 30% of an adhesive such as starch, casein (that is, a caseinate of an alkali metal or ammonium) and the like dispersed in water, and which after drying and calendering is suitable for high grade printing.

A frequent defect of coated paper is the presence of pin holes. Pin holes is the name given to minute, more or less circular openings in the surface of the coating on coated paper. When they are numerous and large, they are very objectionable, as they greatly impair the printing quality of paper, especially for fine half-tone work, which is one of the chief uses to which coated paper is put. Pin holes are due to the presence of foam in'the coating mixture. When the bubbles comprising the foam break after the coating is partially set during the drying operation, they leave holes in the coating which do not flow together. The resulting paper contains pin holes.

Many materials have been proposed from time to time to prevent pin holes, including fusel oil, carbon tetrachloride, etc. These materials, particularly fusel oil, are apparently useful under certain conditions, but they are not always reliable.

It has been found that small quantities of pine oil are very effective in preventing pin holes. Tine oil is cheap, harmless and reliable. It may be added directly to the coating mixture during the process of manufacture or it may be added to the coating mixture just prior to its application to the paper.

Only a very small amount of pine oil is ordinarily required. For example, one to two pints of pine oil in 300 gallons of coating mixture sufiices for all ordinary paper coating mixtures. In case of particularly foamy coatings, the quantity of pine oil may be increased to three or four times the normal.

amount. The quantity of pine oil required Application filed August 30, 1928. Serial No. 303,123.

even in extreme cases is less than the quantity of fusel oil required, and in addition the pine oil is considerably cheaper.

Coated paper is subject to another defect known as grease. 'Grease incoated paper refers to transparent spots in the coating.

One cause of this defect seems to be the failure of the coating mixture to wet the paper in all places.

One of the chief difficulties encountered in the use of agents for the prevention of pin holes is the tendency to cause grease when too much of the agent is used. When pine oil is used this difficulty is not as serious as with other agents heretofore used.

It has also been found that mixing pine oil with a soluble oil such as sulphonated castor oil gives a mixture which when poured into the coating mixture causes the pine oil to be dispersed in an extremely finely divided state. This gives .a much better distribution of the pine Oll than is obtained by adding the pine oil alone. Moreover, the mixture of pine oil and sulfonated castor oil appears to have less tendency to form grease than pine oil alone, particularly when the pine oil is added in excessive amounts.

The following example will serve to illustrate the invention:

2 pints of pine oil mixed with 2 pints of sulphonated castor oil were added to 30 gallons of an aqueous coating mixture comprising 200 lbs.'of a 60% clay paste and 85 lbs. of a 20% casein solution.

When applied to paper raw stock by the usual methods this composition gave a coating' substantially free from pin holes and grease.

I claim:

1. In a process of coating a web of paper with an aqueous mineral coating composition comprising besides an aqueous vehicle mineral pigment in major amount and an adhesive in minor amount, the step of reducing pin hole defects in the resulting coating which consists in dispersing a relatively small but'elfective amount of pine oil in said composition and coating the paper Web with the resulting mixture.

2. A composition for use in making mineral coated paper havin improved pin hole characteristics, comprisi g at least 70% of mineral pigment, an adhesive, and a relatively small but efiective amount of pine oil, dispersed in water.

3. A composition for use in making mineral coated paper having improved pin hole characteristics, comprisingatleast 70% of mineral pigment, casein, and a relatively small but effective amount of pine oil dispersed in Water. I

In testimony whereof, I afiix my signature.

DONALD B. BRADNER. 

